Semiconductor structures and integrated circuits are manufactured using a wide variety of well known techniques. In the manufacturing of semiconductor devices or integrated circuits, active/passive components are formed on a semiconducting substrate such as silicon, and then interconnected in a desired manner.
Resistors are typically formed in such structures using one of two well known techniques. In the first technique, regions of the semiconductor substrate are doped with n- or p-type dopants. This provides conductive regions in the substrate having a desired resistivity. By forming ohmic contacts to a pair of spaced-apart locations in such regions, a diffused region is provided. Such resistors are referred to in the art as diffused resistors.
In the second technique, an insulator layer, i.e. dielectric layer, is formed on the surface of a semiconductor substrate. Next, a layer of polysilicon is formed on the insulator layer. The polysilicon film is either doped in-situ or it is doped with a n- or p-type dopant after deposition of the same. Again, the dopants form a conductive region having a desired resistivity. To complete the resistor, ohmic connections are formed on a pair of spaced-apart regions on the polysilicon layer. These resistors are referred to in the art as polysilicon resistors.
Compared with diffused resistors, polysilicon resistors offer a significant advantage in that they do not consume any area in the semiconductor substrate itself. Thus, the substrate remains available for the fabrication of active components, while the resistor interconnections can be made directly above the active components themselves. Moreover, since the resistor is separated the semiconductor substrate by an insulating layer, the polysilicon resistors have a substantially lower capacitance with the substrate than their diffused counterparts.
One major drawback of such polysilicon resistors is that the polysilicon resistors are sensitive to low temperature variation in excess of about 500.degree. to about 600.degree. C. The exact temperature sensitivity depends on the dopant species found in the polysilicon layer as well as the composition, i.e. grain boundaries and grain size, of the polysilicon itself. Therefore, if the temperature of the back end of the line (BEOL) or later front end of the line (FEOL) process changes, the resistance of the polysilicon resistor will often vary to a value below the targeted resistance. For example, in the development of N+ type polysilicon resistors for BiCMOS, the resistance of the polysilicon resistor dropped by approximately 20% due to changes in the low temperature processing in the range described above.
In view of the above mentioned drawback with prior art polysilicon resistors, there is a continued need for developing new and improved methods which can substantially eliminate the variance in resistance caused by low temperature thermal processing that may occur during subsequent BEOL or FEOL processing. There is also a need for developing a processing method which is capable of providing a controllable resistance to a polysilicon resistor that has a high degree of tolerance for low BEOL and FEOL processing temperatures.